1. Field of the Invention
The present invention relates to an accumulator having a bellows, which is used for pressure accumulation or pulsation absorbing in hydraulic devices in automobile brake systems and various industrial hydraulic systems. The present invention further relates to a manufacturing process for accumulators such as the above, and more specifically relates to a joining method for shells which form a vessel for enclosing oil and gas therein.
2. Background Art
FIG. 5 shows an accumulator used for hydraulic devices in automobile brake systems and various industrial hydraulic systems. The inside of a housing 31 acts as a pressure vessel and is partitioned into a gas chamber 33 in which a compressed gas is sealed therein and a hydraulic chamber 34 by a metallic bellows assembly 32. The metallic bellows assembly 32 comprises an elastic metallic bellows 35, of which one end is fixed to the housing 31 and the free end thereof is equipped with a valve 37. The hydraulic chamber 34 defined in the interior of the housing 31 and exterior of the metallic bellows 35 is communicated with an external system through an opening 38a provided in the housing 31 and a flow path 38.
In such accumulator, when the hydraulic pressure transmitted from the flow path 38 is lower than the gas pressure sealed in the gas chamber 33 and the pressure in the hydraulic chamber 34 coincides with the low pressure, a differential pressure occurs between the gas chamber 33 and the hydraulic chamber 34. As a result, the metallic bellows 35 is extended and the valve 37 is thrust and closely contacted to the circumference of the opening 38a, thereby closing the opening 38a, and the valve 37 therefore self-seals so as to make the pressure of the hydraulic chamber 34 greater that of the gas chamber 33.
The valve 37 may not be able to exhibit sealing properties in closing due to factors such as aging degradation thereof and jamming of foreign matter such as dust. When the pressure transmitted from the flow path 38 is low, the pressure in the hydraulic chamber 34 also becomes low. As a result, stress is generated in the metallic bellows 35 due to the differential pressure between the hydraulic chamber 34 and the gas chamber 33, so that the durability thereof is lowered.
The end plate of the accumulator must be thick since it is slab-shaped, which results in increased weight of the overall accumulator. Therefore, end plates having semicircular or semi-ellipsoid cross section, which can disperse stress, are mainly used.
In accumulators, the stroke of the metallic bellows contained therein is essential for designing the volume of the gas to be sealed therein. The cylindrical portion of the pressure vessel is effective for pressure accumulation. In the end plates having semicircular or semi-ellipsoid cross section, the curved portion is a dead space and is generally employed merely for containing the liquid. Therefore, it has been desired to effectively use this dead space.
The accumulator absorbs pulsation by the elastic motion of the metallic bellows. However, the pressure of the pulsation occurring at a pressure lower than that of the sealed gas is lower than the operating pressure of the accumulator, so that the pulsation cannot be absorbed by the above construction. Heretofore, a special resonance box having a frequency corresponding to the pulsation is provided to absorb the pulsation. This results in large design and increased weight of the accumulator.
The pressure vessel of the accumulator consists of at least two shells for containing the bellows and other necessary parts, and such a manufacturing process is applied so that the bellows and the like are attached to one shell, and another shell is then put over the bellows and the like and is joined to the other shell. In the conventional joining method, the outer surface portion of the joining portion has been welded over the entire circumference by gas welding or tungsten inert gas welding.
However, these welding methods require long operation time, and mass-production efficiency is therefore not good and production cost is relatively high. Therefore, developments in methods for efficiently joining shells have been desired.
An object of the present invention is to improve reliability of self-sealing properties of accumulators. Another object of the invention is to provide an accumulator which can efficiently use the dead space formed by the end plate having semicircular or semi-ellipsoid cross section in the pressure vessel and can absorb pulsation with optional frequency without large design and being heavy. A further object of the invention is to provide a manufacturing process for accumulator, in which shells are efficiently joined, manufacturing time is shortened, and manufacturing cost is decreased.
The invention provides an accumulator comprising: a pressure vessel; an elastic bellows in which a compressed gas is sealed, an end of the bellows being fixed to an interior of the pressure vessel; a flow path having an opening communicating with the interior and an exterior of the pressure vessel; a valve connected to a movable end of the bellows to operatively close the opening according to elastic motion of the bellows; and a hydraulic chamber partitioned from a gas chamber formed in an interior of the bellows containing the compressed gas; wherein the valve comprises an upper surface which can cover the opening, and plural circular protrusions which surround the entire circumference of the opening and can closely contact the circumference of the opening.
Furthermore, the inventors noted that a hydraulic chamber may function as a resonance box according to the frequency of pulsation, and have made the invention based on this. The invention provides an accumulator comprising: a pressure vessel having an end plate curving convexly outward; an elastic bellows having two ends, one of the ends being connected to the end plate of the pressure vessel via a plug member and the other of the ends being closed so as to partition the interior of the pressure vessel into a hydraulic chamber communicated with an exterior system and a gas chamber sealing a compressed gas; and a resonance box formed at the plug member in a location of the end plate so as to absorb predetermined pulsation; wherein the plug member is replaceable.
The invention further provides a manufacturing process for an accumulator, the process comprising: assembling a buffer member into a cylindrical shell so as to partition a interior of the shell into a gas chamber and a hydraulic chamber; and closing the shell; wherein the shell comprises shell portions divided in the direction of an axis of the shell; a circular circumferential portion projecting outward is formed over the entire circumference of each joining portion of the shell portions; a circular protrusion projecting in a joining direction is formed at the circular circumferential portion of at least one of the shell portions; the circular protrusions are brought into contact with each other, or alternatively the circular protrusion is brought into contact with the circular circumferential portion of another shell portion; the circumferential portions are clamped and pressed by a pair of electrodes; and the electrodes are energized so as to join the joining portions by electric resistance welding.
According to the manufacturing process for an accumulator in the invention, the joining portions of the shell portions are directly pressed and clamped by the electrodes. The circumferential portion projecting outward is formed so that the electrodes come into proximity with each other. When the circular protrusion is formed in each circumferential portion, the circular protrusions are brought into contact with each other. When the circular protrusion is formed in one of the circumferential portions, the circular protrusion is brought into contact with another circumferential portion. The electric resistance welding through bringing protrusions into contact each other is called xe2x80x9cprojection weldingxe2x80x9d, in which the welding is performed over the entire circumference with instantaneous energization. Therefore, the time required for welding the shell portions can be greatly shortened compared to the conventional welding method. As a result, mass production efficiency is improved and manufacturing cost can be reduced.